1. Field of the Invention
The present invention relates to a paper feeder for feeding paper with rollers. The feeder may be applied to, for example, an image former, a paper reverser, etc.
2. Description of the Prior Art
FIG. 1 shows a conventional paper feeder, which includes a feed roller 2 and a reverse roller 3. Transmitted to the feed roller 2 through a clutch 7 is torque (in the direction of arrow a) for feeding paper in the feed direction (arrow A). Transmitted to the reverse roller 3 through a clutch 8 is torque (in the direction of arrow a) for returning the paper reversely to the feed direction (arrow A). The reverse roller 3 is fitted with a torque limiter 9, which allows the reverse roller 3 to rotate in the feed direction (arrow b) when one sheet of paper passes between the rollers 2 and 3, but rotates the reverse roller 3 in the reverse direction (arrow a) when two (or more) sheets pass between the rollers. The reverse roller 3 is supported through a lever 5 on a fulcrum 6 and urged by a spring 4 against the feed roller 2. This urging force is so determined that the reverse roller 3 rotates in the reverse direction when two (or more) sheets of paper are fed, as stated above, to prevent double feed.
The construction of this paper feeder is shown, for example, Japanese Utility Model Laid-open Sho 59 No. 187,647 and Japanese Patent Laid-open Sho 63 No. 185,745.
In general, the feed roller 2 and the reverse roller 3 of the paper feeder have a surface of elastic material such as urethane rubber. Accordingly, the surfaces of the rollers 2 and 3 are gradually worn away by their feeding action, thereby lowering the friction coefficients of the rollers. As a result, even when no or one sheet of paper is fed between the rollers 2 and the reverse roller 3 intends to rotate in the direction (arrow a) reverse to the feed direction, so that a misfeed may occur.
As stated above, the reverse roller 3 is urged against the feed roller 2 by means of the spring 4 and the lever 5. If the urging force (contact pressure) is not properly determined, the rollers 2 and 3 will not operate as stated above. For example, if the urging force is too high, the reverse roller 3 will rotate in the feed direction (arrow b) by following the feed roller 2, even though the torque in the reverse direction (arrow a) is transmitted to it. If the urging force is too low, it will be difficult for paper to pass between the rollers 2 and 3, so that a misfeed may occur. Thus, it is necessary to properly determined the contact pressure between the rollers 2 and 3. In the conventional structure, however, the range of the proper contact pressure is narrow and it is thus difficult to adjust the pressure, thereby increasing the costs.